Alignment level
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The alignment level in an audio signal chain or on an audio recording is a defined anchor point that represents a reasonable or typical level.
Analogue
[edit]In analogue systems, alignment level is commonly 0 dBu (0.775 volts RMS) in broadcast chains and in professional audio is commonly 0 VU, which is +4 dBu (1.228 volts RMS). Under normal situations, the 0 VU reference allows for a headroom of 18 dB or more above the reference level without significant distortion. This is largely due to the use of slow-responding VU meters in almost all analogue professional audio equipment, which, by their design and by specification, respond to an average level, not peak levels.
Digital
[edit]In digital systems alignment level commonly is at −18 dBFS (18 dB below digital full scale), in accordance with EBU recommendations.[citation needed] Digital equipment must use peak-reading metering systems to avoid severe digital distortion caused by the signal going beyond digital full scale. 24-bit original or master recordings commonly have an alignment level at −24 dBFS to allow extra headroom, which can then be reduced to match the available headroom of the final medium by audio level compression. FM broadcasts usually have only 9 dB of headroom, as recommended by the EBU, but digital broadcasts, which could operate with 18 dB of headroom, given their low noise floor even in difficult reception areas, currently operate in a state of confusion, with some transmitting at maximum level, while others operate at a much lower level, even though they carry material that has been compressed for compatibility with the lower dynamic range of FM transmissions.[citation needed]
EBU
[edit]In EBU documents[specify] alignment level defines −18 dBFS as the level of the alignment signal, a 1 kHz sine tone for analog applications and 997 Hz in digital applications.
Motivation
[edit]Using alignment level rather than maximum permitted level as the reference point allows more sensible headroom management throughout the audio signal chain; compression happens only where intended.
Loudness wars have resulted in increasing playback loudness. Loudness normalisation to a fixed alignment level can improve the experience when listening to mixed material.
See also
[edit]External links
[edit]- EBU Recommendation R128 - Loudness normalisation and permitted maximum level of audio levels (2010)
- EBU Recommendation R68-2000
- EBU Recommendation R117-2006 (against loudness war)
- AES Convention Paper 5538 On Levelling and Loudness Problems at Broadcast Studios
- EBU Tech 3282-E on EBU RDAT Tape Levels Archived 2009-09-09 at the Wayback Machine
- EBU R89-1997 on CD-R levels[permanent dead link]
- Distortion to the People — TC Electronics
- EBU Loudness Group